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How-To: 15.6 Gallons into Eco MT Tank

76K views 136 replies 40 participants last post by  Jimster480 
#1 · (Edited by Moderator)
Go back to COMG- The Cruze Owner's Maintenance Guide


Here's the definitive way to properly increase your tank capacity from 12.x gallons to 15.x gallons.

First, get the fuel pump module from any 1.4L Cruze as long as it's NOT the ECO M6.

Next step is to release pressure in your fuel lines. I just pushed in the schrader valve that's on the fuel rail and had a rag handy to catch the fuel. After that remove the fuel tank. To do this you have to remove all the ECO specific underbody cladding. There's 3 pieces. 2 that run the length of the car and 1 smaller one that runs side to side by the fuel tank. They're easy to remove, just a bunch of 10mm plastic nuts and 2 10mm bolts.

After those are out of the way I lowered the rear section of exhaust by unbolting it right behind the catalytic converter. Just 2 13mm nuts and it'll lower enough for the tank to clear.

Disconnect the fuel filler hose at the tank, vent tube that's right next to it, main fuel line and vent line next to that.

There are 4 electrical connectors to unplug. 1 is on the vapor canister and this one is the hardest one due to lack of space. 1 is on the fuel line, 2 are on top of the fuel pump module. The only way to get to them is to lower the tank. To lower the tank you just unbolt the 2 straps that hold the tank in. 13mm bolts. I bent them down and out of the way. They're easy to bend and bend back without any damage. The only other way to do this without bending them is to remove the rear axle beam.....you decide. :eek:)

After you're sure all wires and tubes are unplugged lower the tank and slide it out the passenger side. Mine only had a few gallons in it so it was pretty light. DO not do this unless your tank is almost empty.

Once the tanks out and on the ground on top of the fuel pump module there are 2 tubes to unplug.

After that the locking ring is un-done with a punch and hammer. Just tap the tabs counter clockwise and it'll come right off. Once that's off the module just lifts right out.

Put the new one in and everything is reverse order to put it back together.

Enjoy your higher capacity!

Here's some pictures.

Fuel tank out of the car:



ECO M6 12.x gal on left, ECO A6 15.x gal on right:



Here's what it looks like with the tank removed. You can see the straps I'm talking about here:



Exhaust unbolted here to allow it to drop down enough for the tank to clear:



My tank had about 3 gallons in it when I swapped out the modules, here's filling the tank with the nozzle on full throttle after it shut off by itself:



Here's my gauge showing full WITHOUT trickle filling:
 
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#2 ·
My tank had about 3 gallons in it when I swapped out the modules, here's filling the tank with the nozzle on full throttle after it shut off by itself:
Your very accurate with your 3 gallon guess.

On my 1LT I had the low fuel warning come on as I was pulling up to the pump. It took 13.1gallons to fill, that leaves a 2.5gallon reserve when the low fuel warning comes on(assuming 15.6gallon tank size).
 
#7 ·
To do this with "just a few gallons" in the tank is inviting disaster. Gasoline is extremely volatile. When you first lift the fuel pump module out of the tank, the vapor space in the tank above the remaining gasoline will be "rich" - meaning above the upper explosive limit. But as soon as you expose that vapor space to air (by way of the big hole in the tank where you took out the module) the vapor space may very well drop into the explosive range. A gasoline-air mixture in the explosive range is extremely easy to ignite from any tiny spark, including static electricity. If this happens when you are kneeling over the tank, you could be severely burned and injured. And since it is a plastic tank, the tank will be on fire suddenly and depending on where the car is, the flames could spread to the car - and it's mostly plastic nowadays. So, please, please, please - if you are going to attempt this modification, figure out some way to drain the tank completely and then let it "air out" for a couple of hours - go get a Starbucks giant coffee and relax while you relish the idea of going 600 miles between fill ups. Can't drain the tank completely and in too much of a hurry to let it air out? It would actually be safer to do this modification with the tank completely full. This eliminates any vapor space, so there cannot be a vapor-air explosion in the tank. 15 gallons of gas weighs about 90 pounds, so get to the gym and do some bench presses for a few weeks before doing the job with a full tank. Sorry to rain in this parade, but as a Fellow of the Society of Fire Protection Engineers and a Senior Member of the American Institute of Chemical Engineers, I am bound by a code of ethics where I must point out unsafe ideas and practices. The safest way to go 600 miles between fill ups is to get on the wait list for the new Cruze Diesel!! Because I spent my whole career preventing fires and explosions in chemical plants, paint plants, pharmaceutical plants, etc., I don't know how many lives I saved with my recommendations and designs for safe operaations/maintenance procedures, but I may have just saved yours if you were thinking of doing this mod "with a few gallons in the thank." Happy Motoring!!
 
#9 ·
While I agree with Erastumus that the risk of fire is definitely there and that an empty tank of gas is definitely more flammible than a full tank, I also don't think it's a bad as he states. You always have to be careful when working around gasoline - anyone who has tuned a gas lawnmower is aware of this risk. The risk mitigation is to release the pressure from the tank in a controlled and "safe" method. To do this simply open the gas cap before starting. I don't think this modification can be done with a full tank as the tank will tend to rock on whatever surface you place it on thus spilling gasoline out of the tank, raising the risk of fire. I would definitely do this with as few gallons as possible in the tank and only after I had released the tank pressure by bleeding the fuel line to the engine and the fill pipe of extra fuel and vapor pressure.

The part path at GMPartsDirect.com is "All Vehicles - 2012 Chevrolet - Cruze - ECO - Fuel System - Fuel System - Fuel System Components - Fuel pump assy". It's item 9 on the diagram and there are two options - one without 13 gallon fuel tank and one with 13 gallon fuel tank. The fuel pump price is $335.37 MSRP / $174.39 GMPartsDirect.

One question - does the new fuel pump come with a new seal and retainer, and if not, should these be replaced as well?
 
#10 ·
Take caution as you may but i'd love to know how you empty the tank completely then vent it for hours before removing the fuel pump module? I don't know of a single shop nor mechanic who'd attempt that.

Getting it as light as possible "only a few gallons in tank" and common sense should keep things safe. If a person wanted to go all safety overboard you could get some bonding straps, put one on your wrist, the other on the tank and bond both to ground. That would eliminate any chance of static discharge.

Anyways all safety disclaimers aside, I wanted to do this the RIGHT way and I have and wanted to make sure others knew what was needed to do this.

As far as the part number goes I'm sure someone will find it and post it. There's only 2 fuel pump modules for the 1.4L cars. ECO M6 or not. That's it.
 
#11 ·
Very nice write-up however I think I'll just stick to my cheap and simple way of just adding an extra 2 gals (instead of 3) by pouring in the extra 2 gallons from my gas can after my fillup. It goes in as fast as you can pour and cost about $5 (for the gas can).
 
#13 ·
I know GM "W" Bodies such as the Oldsmobile Intrigue had a ball valve check valve assembly as part of the filler tube connection at the tank. On this car you couldn't pass a siphon hose down the fuel filler tube, as you couldn't get by this ball check valve.

In the Olds Intrigue there was an access panel to the fuel tank from behind the rear seats, inside the car, and you could drain the tank from there.


firehawk- Did you notice a check valve on the filler assembly near the tank? If I recall Alldata says drain the tank, but doesn't say how.. Therefore I'd assume it would be out the filler tube, but be carefull. If your siphon hose hits resistance, your up against that check valve assembly.. Don't break it.
 
#16 ·
There's no check ball on our filler neck that I could see *didn't look* BUT what does prevent siphoning is a screen right where the filler tube enters the tank.
 
#14 ·
Thanks for pioneering this! Looking at the photos of the fuel pump assemblies, it looks as though you may be able to remove the black clip from the Eco pump assembly to raise the float or valve. If you get a chance, could you take a look at your original pump and verify if this is true or not?
 
#17 ·
I don't see any adjustment at all. The float thingey is totally different between the 2 modules. It does look like if you could get your hands on the proper float thingey it would clip right onto the other module. I am willing to bet you cannot buy that piece by itself, you must buy the whole thing. Fortunately used they're not too spendy really and if you look a little bit a low mile one can be found easily since our cars are still fairly new.


The bright side to buying a whole replacement module to do this mod is you'll now have a spare fuel pump, sending unit and tank pressure sensor if any should ever fail.

I don't believe GM sells the pump only, most manufacturers don't anymore but you can take the module apart and swap out just pumps.
 
#18 ·
Next venture: Factory heated mirrors, factory heated seats.
 
#24 ·
I was considering this until I filled up Penguin LS this evening. $50 later I was in pump sticker shock. I'll stick with the 12.6 easy limitation which keeps my fill ups below $40.
 
#29 ·
I wonder why in the world would they spec a different tank for fleet vehicles?
 
#31 ·
Great write-up! I was actually pretty curious about this, nice to see someone else did it before I did.

I'm gonna have to do this when it starts getting warm outside..
 
#32 ·
It's a cold winter's night. You have a heated garage - forced hot air. Right after you take the fuel pump module out, your cell phone rings. It's the boss and he has a major issue to discuss. You go in the house and make a cup of coffee and put the boss on speakerphone. A half hour later, you return to drop the new module in. The hot air furnace calls for heat - VAROOM - the gasoline vapors have traveled over to the furnace, hugging the floor all the way because they are heavier than air and the flame flashed back to you and the gas tank. Pants on fire. I have issued my warning and stated my credentials. I will let it rest now - each of you who decides to do this after reading this entire thread has done so of a free will. Remember the laws of tort in the U.S. - juries almost always find for the plaintiff - firehawk618 and obermd could end up being be found culpable if a forum member gets hurt and sues those who led him/her to the injury. And I might be called to the trial as an expert witness - been there, done that.
 
#33 ·
Why would you be doing this in a non-ventilated enclosed space. You never, ever, work around volatile liquids in a non-ventilated enclosed space. This is safety rule number one when dealing with volatile liquids. I have yet to see any home garages that don't qualify as a non-ventilated enclosed space when the garage door is closed. I wouldn't even fill a gas lawnmower in a garage without the garage door being open. As I said earlier, you must be careful when working around gasoline.

In addition, unless you have a car lift or service pit in your garage, this is not a mod you want to do because of the amount of under vehicle work you have to do. Putting the car up on ramps isn't sufficient to do this job properly - they aren't high enough. By itself this requirement will prevent most people from even attempting this mod in their garage. It needs to be done somewhere where you can move yourself and large pieces of equipment around under the car.

By the way - your scenario would also include someone filling their gas tank on their way home from work, forgetting to put the cap back on, and then parking in their garage for the night. I see someone every couple of months driving down the freeway with the gas cap dangling on the side of their car. Gasoline vapors escape from tanks this way, which is why the Check Engine Light will light up after a few miles of this, but if your station is less than about 20 miles away the CEL won't trigger - it takes several consecutive failed pressure check cycles to detect and report the tank vapor pressure loss.
 
#35 ·
Can someone explain HOW changing the tank unit will give you 3 gallons more capacity? I really don't know why Chevy did this on the Eco, gas weighs 6 pounds a gallon, I can't see how that little bit of weight savings along with the spare delete ups the mpg in any way.

Also as far as safety goes, gas tanks are opened every day in service shops indoors.
 
#41 ·
The tank itself is the same across all models, it wouldn't have met cost/benefit to have two different tanks, one for which would only go into about 10% of the cars manufactured. The difference is in the tank vent float, the Eco manual closes the vent at 12.6 gallons instead of 15.6, causing the pump to stop filling. It probably only cost pennies to switch the floats on the pump assembly.

They were looking for every single pound they could get, and this was essentially free weight reduction since most cars are designed around a 400 mile tank range and the 12.6 gal gives better than that.
 
#36 ·
Take a look at the two fuel pumps in the first post. The ECO MT pump has a longer "neck" on the fill level sensor vent, which results in the vent being closed off three gallons earlier.

As for why, sciphi said it best - it takes more energy to start moving a heavier car. By reducing the weight on the ECO MT (less gas capacity, no spare tire, no rear cupholders, etc) GM was able to reduce the weight of the car and mathematically increase city MPG, which in turn increases the all important CAFE number that the US Federal Government uses to determine whether or not a car manufacturer is meeting their requirements for fuel economy. The reality is that most ECO MT drivers spend their time on the open road so the city MPG is much less important to us, meaning the weight reductions are useless.

In reality, adding the spare tire to my ECO MT has NOT impacted my overall fuel economy.
 
#37 ·
The reality is that most ECO MT drivers spend their time on the open road so the city MPG is much less important to us, meaning the weight reductions are useless.
Word!
 
#38 ·
Erastimus, always gotta be a buzz kill in the bunch.

If someone blows themselves up and sues me because of my how to then I guess I'll be in court.

This is a shining example of what's wrong with our justice system. No-one wants to take accountability for their own actions. I refuse to put a stupid disclaimer on my information to *cover my butt*. If a person doesn't have common sense then the way I see it is natural selection. Survival of the fittest.

Oh man, might as well throw out there to not use your scissor jack when doing this job. Oh yes, also, don't forget to breathe while working on this mod.

Check your local weather report before starting for lightning storms because when you have the tank out if lightning hits your shop it could cause the tank to blow. Look for any earthquake activity also because if one strikes when you're under the car whether it's on a lift or jack stands it could crush you.

Carry on.
 
#40 ·
On second thought.....

DO NOT DO THIS MOD, IT COULD BE FATAL!!!!!!

Phew, I feel better. I couldn't live with myself if someone was crazy enough to swap their fuel pump module and killed an innocent kitten.

Ok I feel better now
 
#45 ·
I do have such a scan tool but haven't check. I can check in the next day or two if you like. It's been over 200 miles and no CEL. I'm confident all readiness flags have been set by now and if there was any evap errors a CEL would be lit.
 
#44 ·
I have a 1.4 tank out of a 2012 LT that I bought for $150. The car only had 50 miles on it when it was totaled. I'm sure it will be easy to find low mileage used tank assemblies or modules since these cars are still pretty new. I plan on putting the LT module in my '12 Eco when the weather gets a little better. I did pull the module out of that tank, and it has the red vent valve in it. For whatever reason, the baffles came loose in this tank, and I thought maybe the module had broken. The baffles are spring loaded, and I was able to snap them back into place. Maybe the straps crush the tank a little to help hold them in place. I'll document if I find any other differences in parts.
 
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